The present invention relates generally to the field of power electronic devices, and particularly to implementing diagnostics and prognostics for electric motor drives based on a measured drive inlet temperature.
A myriad of applications exist in industry for motor drives of various types. In many applications, a motor drive includes a circuit for driving an electromagnetic machine, such as a brushed or brushless motor, stepper motor, or other electromechanical actuator. Such motors and actuators may be internal to or external from their respective motor drives. Multiple motor drives may be positioned across various parts of a factory or manufacturing site. In the case of higher power applications, multi-phase motors are commonly used with separate motor drives that may be positioned in cabinets in the general vicinity of the driven motor.
Motor drives generally are designed to output only a certain percentage of a maximum power rating for the device. When new, and during most of the useful life of the machines, the power rating may remain as initially assigned, although some derating may be in order due to environmental conditions, machine age, and other factors. That is, the motor drive is derated from a maximum current output to meet a derating requirement specific to the motor drive, effectively lowering the output of the drive and motor. This derating requirement may be different when the motor drive is operated at different ambient temperatures, which may adversely impact both the performance of the machines, as well as shorten their useful life. In addition, a number of prognostics may be determined for the motor drive based on the ambient temperature at which the motor drive operates.
To perform calculations of various diagnostics, prognostics, and so forth, motor drives often include temperature sensors located on a circuit board of the motor drive. Such temperature sensors are usually buried inside the motor drive itself, enclosed by a protective housing and surrounded by elements that may affect the temperature measurement. In some motor drives, a processor estimates the ambient temperature measurement from the internal operating temperature of the motor drive by applying an energy balance equation. This estimate may be very accurate upon initial operation of the motor drive. Unfortunately, over time this estimate may become less accurate because of operational inefficiencies and degradation of internal cooling mechanisms of the motor drive. Accordingly, it is now recognized that it is desirable to have a motor drive with improved ambient temperature sensing, in order to provide more accurate motor drive diagnostic and prognostic information to a user.